Jamie will be in the three seat, Ollie in the seven on Sunday evening - Geoff Pugh Photography Ltd Telegraph Media Group Ltd

They could only be brothers: the way they laugh, the way they joust, the way they finish each other’s sentences.

Ollie is the more imposing of the two: taller, heavier, blonder, with a deeper voice and a deeper set. Typical older brother.

Jamie, meanwhile, does most of the joshing and most of the talking. Typical younger brother.

The Cancer Research UK Boat Race is one of the toughest races in British sport. Eighteen minutes of unstinting exertion. Eighteen minutes of pure pain. So it helps to have a familiar face along for the ride.

Jamie Cook will not see his older brother four seats behind him in the Oxford boat, but he will hear him, sense him, take comfort from him. When you have blood on your side, the sweat and the tears take care of themselves.

Ollie, 26, is the one with the international pedigree, having won World Championship gold last year and come within a hair’s breadth of earning selection for the Rio Olympics. Jamie, 24, is the one with the race pedigree, having rowed for Oxford in the 2015 and 2016 crews.

View photos

The Oxford crew out on the water earlier this weekCredit: Getty Images

Yet when they take their places on the start line Sunday afternoon, they will know that neither would have made it there without the other.

Like all brothers, there is a healthy rivalry there. As Jamie puts it: “Ollie has always done things. And I’ve always said, ‘Yeah, I can do it better than that’. I’m always the underdog, the younger brother.”

“I know that Jamie’s always trying his best,” Ollie says. “That forces me to be at my best as well.”

“We both started rugby at quite an early age,” Jamie remembers. “We used to play for Windsor, and our father would give us 20p for every tackle we made.”

“There was a good tuck shop where you could spend the money afterwards,” Ollie interjects.

“Ollie’s game would normally be before my game,” Jamie continues, “so Dad would always tell me how many sweets Ollie got. And I would just go berserk trying to beat that number. It’s something that’s always there. There’s a surface of real competition.”

Beneath the surface, however, there is something stronger that binds them together, a link forged as much in adversity as in triumph.

Twelve months ago, Jamie was in the Oxford crew that lost the Boat Race by two lengths. It was, he says now, “one of the most difficult times of my life”.

Afterwards, he resolved that his days in the sport were over. “I was completely done with rowing,” he says. “I didn’t want to do it again. When you lose a race like the Boat Race, that’s your whole year.

“You’ve given up everything: girls, all your academic requirements, all for one race, and you lose. It’s like a child has been ripped away from you. I was devastated for a long time afterwards.”

Standing in the Oxford boathouse watching the race, Ollie was overcome by a strange and uncontrollable anguish. “It was really difficult,” he says. “Because I couldn’t do anything about it. I wanted to be in that boat. To make sure he wasn’t going to lose. I told myself then that I was going to make sure that if Jamie wanted to row again, I’d be there.”

A few months later, the roles were reversed. Having spent four years slogging away in an attempt to make the British team for Rio, Ollie just missed the cut.

“I was the guy that didn’t get selected for the Olympics,” he says. “I trained with those guys for four years. Seeing the guys racing and getting the kit, you feel amazing for them. But you are very aware that it’s not you.”

Reeling from their respective setbacks, the Cook brothers sought solace and strength in a familiar place: each other. With the help of a supportive family, Jamie got over his heartache and set about winning a place in the 2017 Blue boat. Ollie won a place at Christ Church College and set about joining him.

It was, Jamie reports, the toughest selection process he has ever endured.

“We do this thing called the Step Test,” he recalls. “It’s brutal. Every four minutes, you increase the intensity, until you’re flat out on the floor. The whole test lasts 30-40 minutes. I remember I was on my final four-minute step, going absolutely flat out, and Ollie wanders in.”

“Still slightly hung-over,” Ollie chips in.

“And suddenly,” James continues, “I just switched into a new gear. I was like, ‘f--- this, I’m going to absolutely kill myself’. There’s this greater power. Just knowing that I’m not here alone. It’s not just an erg test, it’s not just a race. It’s much more special.”

And so, here they sit: Jamie in the three seat, Ollie in the seven. And whether their journey ends in victory or defeat, it will be all the richer for having been shared. This, after all, is the very essence of sporting fraternity: a bond as common as water, and as thick as blood.